Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.79   11.336%   $96.6285   $96.63   $96.65   $96.60  
  Purchase #2 $226.75   9.396%   $248.0554   $248.06   $248.05   $248.10  
  Purchase #3 $192.86   12.382%   $216.7399   $216.74   $216.75   $216.70  
  Purchase #4 $37.99   8.178%   $41.0968   $41.10   $41.10   $41.10  
  Purchase #5 $174.34   6.721%   $186.0574   $186.06   $186.05   $186.10  
  Purchase #6 $159.73   9.395%   $174.7366   $174.74   $174.75   $174.70  
  Purchase #7 $96.89   8.805%   $105.4212   $105.42   $105.40   $105.40  
  7 purchase totals = $975.35       $1,068.7358   $1,068.75   $1,068.75   $1,068.70